The invention concerns a crash barrier designed as equipment for highways or any other traffic routes to protect vehicles that are driven on them from the risk of a possibly dangerous highway exit.
More precisely, the invention concerns a crash barrier of the type that comprises posts driven into the ground and spaced apart from each other, and wooden rails connected end-to-end with each other and fixed on the posts so that they connect between them, each rail presenting a longitudinal axis with wooden fibers oriented along the longitudinal axis, a front external surface turned toward the highway and a rear external surface turned towards the posts and being substantially reinforced along its length by synthetic fibers forming at least a first cover that extends parallel to the longitudinal axis.
More generally, the crash barriers conventionally used are composed of several rails connected end-to-end to form a continuous and approximately horizontal part, these rails being fixed by bolts to posts which are spaced apart and driven into the ground.
These barriers most often include metallic rails, wooden rails or even wooden rails reinforced by a metal part.
In the case of a vehicle impacting the barrier, the role of the barrier is first to absorb the dynamic energy of the vehicle to prevent the latter from rebounding violently onto the highway or even being quite damaged.
This energy is essentially absorbed by posts that became deformed if they are metallic or which break if they are wooden.
Moreover, the approximately horizontal continuous part formed by the rails should not be totally broken, even at the point of impact of the vehicle on the barrier. This part tightens as soon as the posts are deformed, but remains intact, to enable the vehicle that has left the highway to be progressively brought back to it while stopping it from falling down a highway embankment or even into a ravine.
Barriers comprising wooden rails present numerous advantages but also several defects that need to be corrected.
In fact, wood is a material that has a fragile elastic behavior in tension and plastic elastic behavior in compression. The impact of the vehicle on the barrier is expressed by a tensile force in the rails on the side opposite the impact.
Under these stress conditions, the tension zone ruptures and, by propagation of the cracks, may cross the rail(s) concerned and break them completely. Even pinewood, in which the plastification phase is relatively high, does not guarantee the integrity of the barrier in case of impact.
That is why barriers, including wooden rails, are traditionally best used on highways where the impact is low, for example, on mountain roads or on portions of the highway on which vehicles are only allowed to travel at a much reduced speed.
Reinforcement of wooden rails has already been proposed, using metallic fittings integrated in the rear of the rails, that is, on the side of the posts. Reference may especially be made to the document FR-2 717 196.
Subject to presenting sufficient and well-conceived reinforcement, such barriers can ensure the same safety conditions as metal barriers, while being more friendly to the environment. They therefore provide full satisfaction.
However, they include the drawback of being relatively heavy because of the presence of metallic reinforcement parts, which poses problems during transport and installation of the barriers. The cost of these barriers is also relatively high.
The German utility model DE-G-94 05 557.2 describes a wooden barrier that uses, as rails, wooden logs longitudinally sawn into two halves, between which is provided a single flat metallic bar, the elemental form of such a reinforcement limiting the increase in weight and cost.
Nevertheless, not only does such a barrier remain relatively heavy and expensive, but the flat metallic bar, under the described conditions of use, presents too low a resistance to fulfill any function other than only maintaining integrity of the rail in case of impact.
Moreover, from the patent document EP 0 924 346 a wooden barrier of the first type mentioned above is known, that is, in which the rails are reinforced by synthetic fibers.
Unlike close material, the barrier described in this document has the same structure as the barrier described in the German utility model DE-G-94 05 557.2, namely that it uses wooden logs longitudinally sawn into two halves as rails, between which is provided a layer of synthetic fibers for reinforcement.
The barrier described in the patent document EP 0 924 346 compared to the barrier of the German utility model DE-G-94 05 557.2 obviously benefits from a reduction in weight and inherent expense by changing the material used. On the other hand, the sheet of fibers can only supply this barrier with still less resistance than that supplied by the flat metallic bar on the barrier of the German utility model DE-G-94 05 557.2.
In this context, the present invention especially has the goal of proposing a relatively light and less expensive barrier using wooden rails, and in which the rails nevertheless present an increased resistance, effectively making it possible to bring back to the highway any vehicle that has left it.
To this end, in the barrier of the invention at least some of the fibers of a first cover of each rail are glued to the rail and oriented along the longitudinal axis and arranged at a distance from the longitudinal axis of the rail, with greater proximity to the rear external surface than to the front external surface of this rail.
In other words, instead of being arranged on the neutral axis of the rail as in the patent document EP 0 924 346, that is, exactly between the zone in which, in case of impact, the rail undergoes tension and the zone in which it undergoes compression, the fibers organized in conformance with the invention, on the one hand, offer resistance to the tensile stresses that are added to that of the wood and, on the other hand, ensure the cohesion of the wooden fibers over a significant depth, which has the additional effect of increasing the elasticity of the rail in its entirety.
In one production method of the invention, the first cover of fibers of each rail extends in a plane parallel to the horizontal axis and separates the rail into a front part turned toward the highway and a rear part turned toward the posts, the front part being thicker than the rear part.
Preferably, the synthetic fibers used are fibers that have a high mechanical performance and especially present a tensile strength at least twice as great as that of wood.
The synthetic fibers fixed on the rail by gluing are advantageously glued with a resin.
Moreover, the rail advantageously has between the first cover of fibers and its front external surface a circular cross-section or a cross-section with a circular segment such as a semi-circle.
In order to dimensionally stabilize the transverse section of the rail, some of these fibers are advantageously oriented at least along a direction making an angle with the axis of the rail that is not zero.
Preferably, the GSM of the fibers is greater at the level of the fixation zones of the rail on the posts than on the rest of the rail, so as to limit the risks of splintering in the fixation zones where significant forces are locally concentrated, principally around the means for fixation of the rail on the post.
Fibers may be also fixed on the upper part of the rail, exposed to the weather, to increase the durability of the wood.
Moreover, a cut is advantageously made in the lower part of the rail, to free the stresses due to shrinkage of the wood, which is naturally produced in the wood when it dries, and to thus avoid the formation of cracks on the periphery of the rail.
In a preferred method of production, at least part of the fibers is placed on the entire external surface of the rail.
In particular, these fibers may form a tubular fabric added to the wooden rail and then fixed on the latter.
In fact, as the wood of the barriers is normally subjected to the weather and to attacks by destructive organisms like fungi or insects, it must undergo a treatment, especially with metal salts, to increase its durability.
When the barriers are taken down, the wooden rails must be recycled to limit pollution due to metal salts with which the wood is impregnated and which are very toxic.
The expenses brought about by recycling treated wood are very high since they are approximately three times greater than the price of natural wood itself.
Thus, the fact that the only known treatments designed to increase the durability of the wood require the use of polluting substances forms another very important drawback.
This drawback, which moreover exists not only for wood intended for the production of barriers, but also for all wood used outside, such as that used for the construction of fences or even for playgrounds, arranged for example in squares, may thus be eliminated by enclosing the wooden rail in a sleeve of synthetic fibers, in which the fibers adjacent to the rear surface of the rail considerably reinforce the resistance of the latter.
Finally, fibers may be provided, without being fixed, between the wood of the rail and fibers glued to the rail.
The synthetic fibers used may be especially fibers of glass, carbon or Kevlar(copyright) or even a mixture of these fibers.